cc -pthread  -Wall -Wextra -Werror=implicit-function-declaration unistd/dup3.c -o unistd/dup3 -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread  -liconv
unistd/dup3.c:10:7: error: call to undeclared function 'dup3'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   10 |         if ( dup3(2, 42, O_CLOEXEC) < 0 )
      |              ^
1 error generated.